1. Field of the Invention
The present invention relates to composite substrates, semiconductor devices, and methods for manufacturing semiconductor devices.
2. Description of the Related Art
One of the approaches for achieving high-speed, low-power semiconductor integrated circuits is to employ integrated circuit technology on composite substrates, including SOI technology (see PTL 1). Composite substrates are composed of a support substrate and a functional layer (semiconductor layer). The use of monocrystalline substrates as semiconductor layers for composite substrates provides a high-quality functional layer. In addition to monocrystalline substrates, polycrystalline substrates have also been proposed for use as support substrates for cost reduction. Examples of such composite substrates include silicon-on-insulator (SOI) wafers and silicon-on-sapphire (SOS) wafers for radio-frequency components for cellular phones. With the recent trend toward miniaturization, the development of low-profile radio-frequency devices is becoming more important. Unfortunately, it is known that composite substrates, which are composed of different materials bonded together, are more prone to warpage as they become thinner, which causes problems with device fabrication. Accordingly, backgrinding has recently been employed, in which all functions are implemented on the semiconductor layer before the support substrate is ground to the desired thickness.